*exit-on-eof*

When the top-level read-eval-print loop reads an EOF (end of file,
simulated by Control-D on some systems), the action of Allegro CL
depends on the value of this variable. If *exit-on-eof* is t, Lisp will exit. If it is nil (which is the default), the user will be asked if
he really wants to exit Lisp. If it is a positive integer, Lisp will
exit after exactly that number of consecutive EOFs. Any value other
than nil or a positive integer is equivalent
to the value t. EOF calls exit with no arguments.